Re: [PATCH] cpu/hotplug: Fix rollback during error-out in takedown_cpu()

[Mukesh Ojha]

On 9/4/2018 12:03 PM, Neeraj Upadhyay wrote:

If takedown_cpu() fails during _cpu_down(), st->state is reset,
by calling cpuhp_reset_state(). This results in an additional
increment of st->state, which results in CPUHP_AP_SMPBOOT_THREADS
state being skipped during rollback. Fix this by not calling
cpuhp_reset_state() and doing the state reset directly in
_cpu_down().

Fixes: 4dddfb5faa61 ("smp/hotplug: Rewrite AP state machine core")
Signed-off-by: Neeraj Upadhyay <neer...@codeaurora.org>
---
  kernel/cpu.c | 9 ++++++++-
  1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index aa7fe85..9f49edb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -970,7 +970,14 @@ static int __ref _cpu_down(unsigned int cpu, int 
tasks_frozen,
         */
        ret = cpuhp_down_callbacks(cpu, st, target);
        if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) {
-               cpuhp_reset_state(st, prev_state);
+               /*
+                * As st->last is not set, cpuhp_reset_state() increments
+                * st->state, which results in CPUHP_AP_SMPBOOT_THREADS being
+                * skipped during rollback. So, don't use it here.
+                */
+               st->rollback = true;
+               st->target = prev_state;
+               st->bringup = !st->bringup;

Acked-by: Mukesh Ojha <mo...@codeaurora.org>

looks valid for this case.

                __cpuhp_kick_ap(st);
        }